1. Technical Field
The present invention relates to a solid oxide fuel cell unit. In particular, the present invention relates to a solid oxide fuel cell unit that is gas-tightly fixed to a fuel gas tank, the solid oxide fuel cell unit having a joint portion which provides the gas-tight fixation and which is highly reliable against repetition of operations of the solid oxide fuel cell unit where the solid oxide fuel cell unit is activated by raising a temperature from room temperature to high temperature and is stopped by lowering a temperature from high temperature to room temperature.
2. Background Art
A solid oxide fuel cell (hereinafter also referred to as “SOFC”) includes a solid-oxide ion-conducting electrolyte as the electrolyte, and electrodes are attached to both sides of the electrolyte. The fuel cell is operated at relatively high temperature by supplying a fuel gas to one electrode and an oxidizing agent gas (air, oxygen, or the like) to the other electrode.
A solid oxide fuel cell apparatus, especially, a fuel cell module housing solid oxide fuel cell units comprises a fuel flow path for supplying a fuel to the solid oxide fuel cell units, an oxidizing agent gas flow path for supplying an oxidizing agent gas such as air thereto. In general, these flow paths are constituted of multiple constituent members. The flow paths are formed by joining the constituent members together. In addition, since solid oxide fuel cells are generally operated at high temperature of 600 to 1000° C., the joints of the solid oxide fuel cell units to constituent members (for example, a fuel gas tank) have to withstand such high temperature.
Japanese Patent No. 5173458 proposes a cell in which an electrically conductive lead film (Ni—MgAl2O4) is formed on a surface of a substrate tube (15% calcia-stabilized zirconia) and a gas-tight film (8% yttria-stabilized zirconia) is formed on a surface of the lead film, wherein an adhesion-improving film having an appropriate thermal expansion is provided between a surface of the gas-tight film and an adhesive agent.
Japanese Patent No. 5080951 refers to a distance between a current collector and an active fuel electrode layer provided on a fuel electrode in a solid oxide fuel cell unit comprising a plurality of power generation elements in order to suppress peeling of an internal electrode and the like and formation of cracks and the like.
Japanese Patent Application Publications Nos. 2010-257744 and 2008-59793 disclose views showing how cells arranged upright are gas-tightly joined to a fuel gas tank.
Japanese Patent No. 3064087 proposes a method for producing a solid electrolyte cell, in which simultaneous calcination of a substrate tube, and a part or the entirety of an electrode and an electrolyte makes it possible to achieve stability in performance and reduce the man-hour of the production.
Moreover, Japanese Patent No. 5188236 proposes a gas supply/exhaust manifold which can simplify the gas supply/exhaust structure. Cells are inserted through insertion holes formed in plates of an insulating material, and are sealed by gas seal members.